1. Field of the Invention
The present invention relates to a miter saw, and more particularly to a miter saw of the type called "slide saw" in which a miter saw unit having a saw blade mounted thereon is slidably movable in a horizontal direction relative to a base for placing a work thereon.
2. Description of the Prior Art
A conventional miter saw of this type includes a slide support mechanism for slidably supporting a miter saw unit relative to a base. The slide support mechanism includes a holder mounted on the base and a slide bar mounted on the miter saw unit. The slide bar is inserted into a guide hole formed on the holder and is supported by the holder directly or via a linear guide bearing.
In order to prevent the holder from rotation relative to the guide bar, a pair of the slide support mechanisms are provided in juxtaposed relationship with each other.
Japanese Laid-Open Utility Model Publication Nos. 62-162001 and 3-129401 and U.S. Pat. Nos. 4,869,142 and 5,146,825 disclose such pair of slide support mechanisms.
U.S. Pat. No. 5,054,352 in the name of the same assignee as the present application discloses the provision of a support shaft fixed to a slide bar in a diametrical direction. A first and a second bearing are mounted on an end projection of the support shaft and have central axes extending coaxially with and eccentrically from the axis of the support shaft, respectively. The first and second bearings are received in a guide rail formed on a turntable mounted on a base, so that the slide bar is effectively prevented from rotation relative to the base.
In case of the provision of a pair of the slide support mechanisms, a support portion having such juxtaposed pair of the support mechanisms must have a larger size in a lateral direction. Therefore, if such a support portion is adopted to a miter saw which is operable to obliquely cut a work with the support portion as well as a miter saw unit inclined in a lateral direction, the support portion may be interfered by the base as the inclination angle of the miter saw unit increases, so that an oblique cutting operation cannot be effectively performed.
Further, when the miter saw unit is pulled forwardly to perform the cutting operation in the horizontal direction, the pairs of the support mechanisms are moved at a position above the work, so that the support mechanisms may abut on the slide bar, the turntable, a fence member for positioning of the work or the work itself even if the inclination angle is relatively small. Therefore, the miter saw is not operable to cut a work having a larger thickness and is not operable to cut the work, with the miter saw unit inclined to a large extent.
In case of U.S. Pat. No. 5,054,352, although the rattling can be effectively prevented, the construction becomes rather complicated because of the provision of a particular mechanism including the support shaft, the first and second bearings, etc.
Meanwhile, with this kind of support mechanism, a slide bar is exposed on both sides of a holder in a longitudinal direction. In order to prevent deposition of dust on a sliding surface of the slide bar or in order to prevent the sliding surface from rusting, such exposed parts of the slide bar are normally covered by bellows. More specifically, two parts of the slide bar between the forward end of the slide bar and the forward portion of the holder and between the rear portion of the holder and the rear end of the slide bar are covered by the bellows. These bellows are cylindrical in configuration and form therein spaces closed from the outside.
Because of such closed spaces formed in the bellows, as the slide bar is moved to compress one of the bellows and to expand the other of the bellows, the air within one of the bellows are compressed, so that the slide bar cannot be smoothly moved. In order to obtain smooth movement of the slide bar, air holes each having a smaller diameter are formed on the bellows to permit the air within the bellows to be exhausted and absorbed as the bellows are compressed and expanded.
However, with the provision of the air holes, dust may enter the spaces within the bellows as the air is absorbed into the spaces through expansion of the bellows. Therefore, the aimed function of avoiding dust or rusting cannot be sufficiently performed.
Further, since the bellows thus perform the operation called "respiration", an unpleasant respiration sound is produced as the slide bar is moved.
Additionally, although the provision of the air holes may permit smooth movement of the slide bar to some extent, it is preferable that each air hole has a smaller diameter to ensure the aimed function of the bellows. For this reason, each air hole normally has an extremely small diameter, resulting in that the smooth movement of the air in and out from the bellows is prevented. Therefore, the smooth movement of the slide bar as well as the miter saw unit is limited to some extent. Particularly, as the speed of movement of the miter saw unit is increased, the resistance produced by the air is increased to prevent smooth movement.